1. Field of the Invention
The present invention relates to a magnetron filter apparatus and particularly to a structure of magnetron filter apparatus just suitable for a microwave range to be operated with a high frequency driving power supply.
2. Description of the Prior Art
FIG. 1 shows a basic concept of a power supply for driving a magnetron. In FIG. 1, numeral 1 denotes a commercial power supply of 50 or 60 Hz which generates a cathode current and a voltage to be supplied to the magnetron 3 with a transformer 2. 4 is a smoothing capacitor and 5 is a rectifying diode. The section enclosed by the dotted line 6 is a magnetron 3 designed with an ordinary structure. The section enclosed by the dotted line 7 is a filter apparatus integrally provided to the magnetron 3, which eliminates unwanted waves (mainly, TV noise) generated for the magnetron 3 with inductance of a choke coil 8 and a through capacitor 9.
Recently, development and investigation for practical use of a so-called inverter power supply which converts the frequency of a commercial power supply to the high frequency of 10k.about.100 kHz and thereby makes possible remarkable reduction of the size of a transformer required are showing dynamic advancement.
FIG. 2 shows a conventional magnetron filter apparatus. A bottomed box type filter case 16 is forced to engage with a cylindrical seal 10 of the magnetron bulb and a couple of leads 12 which support the cathode in the bulb are hermetically brazed together with terminals 13 through a stem ceramic 11 hermetically brazed to the cylindrical seal 10. The terminals 13 are respectively fixed with choke coils 8 wound around the ferrite core, with the other ends thereof connected to a through capacitor 9. This through capacitor 9 is fixed to a filter case 16 through a chassis plate 9a which is earthed. Moreover, a cover 17 is fixed to said filter case 16 by caulking the four sides thereof in order to shield unwanted waves such as harmonics of a magnetron. Above structure corresponds to the section enclosed by a dotted line 7 in FIG. 1. Usually a cathode current to be supplied to the terminals 12 of a cathode in the filter case 16 is comparatively as high as 10.about.16 A in the case of a magnetron and therefore a lead wire as thick as 1.0.about.1.6.phi. is necessary. Moreover in case of a commercial power supply it is disadvantage because a transformer itself becomes large in size due to its low frequency (50 or 60 Hz) to attempt to include said transformer which supplies the cathode current within the filter case 16.